Short answers, pulled from the story.
The Mitsubishi A6M Zero, designated the Type 0 Carrier Fighter by the Imperial Japanese Navy, entered service in 1940. It was named Zero because it was the last digit of the Imperial year 2600.
Chief designer Jiro Horikoshi created the Mitsubishi A6M Zero with a philosophy that prioritized extreme lightness and maneuverability over protection. He used extra super duralumin alloy and omitted armor for the pilot and engine to meet demanding speed requirements.
Allied forces captured a Mitsubishi A6M Zero on the 4th of June 1942 after Flight Petty Officer Tadayoshi Koga crash-landed on Akutan Island. The aircraft was shipped to Naval Air Station North Island where testing revealed its fatal flaws.
The Mitsubishi A6M Zero lost its dominance due to deteriorating Japanese pilot training and the introduction of superior Allied aircraft like the Grumman F6F Hellcat. New tactics such as the Thach Weave exploited the Zero's inability to roll quickly and its vulnerability in dives.
Over 10,000 Mitsubishi A6M Zero aircraft of all variants were produced, making it the most numerous Japanese fighter of the war. Production continued until 1945 with the A6M7 variant entering service in May 1945.